The present invention relates to spatially selective audio reproduction, e.g. of different audio signals to different listeners or groups of listeners who are located in different positions.
Reproduction of audio signals via several loudspeakers typically organized as an array is a common method. By replicating the signal and by obtaining the loudspeaker signals by means of individual modification, e.g. by imposing a delay and a change of the amplitude, which generally can also be described as filtering, the shape of the sound field radiated by means of a loudspeaker can be influenced in a target-oriented manner, for example for the purpose of exposing specific regions to sound in a targeted manner. Said techniques will be referred to as beamforming below. By means of this technology, it is also possible to simultaneously reproduce several audio signals with different directivity characteristics by producing, for all signals, individual filtered loudspeaker signals that are summed up, loudspeaker by loudspeaker, prior to reproduction. In this manner, spatially selective reproduction may be achieved wherein several regions, so called “sound zones”, are sonicated with different signals, mutual influencing of the sound reproduction among said sound regions or with other zones, so called “quiet zones”, which are intended to be silent as much as possible, being minimized.
There are a multitude of algorithms for determining beamforming filters. In addition to those applying only amplitude weights and/or delays, there are also methods that are based on frequency-dependent filtering. Said methods are often based on optimization techniques and enable flexible default of a desired radiation behavior, such as a selectable radiation direction or the suppression of the radiation within definable regions, in accordance with the above-mentioned “quiet zones”.
Notwithstanding such beamforming algorithms, the effectiveness of spatially selective sonication (exposure to sound), in particular of the suppression of the audible interference between sound zones, is often limited and allows no acceptable quality. The main reasons for this are the limitations of the loudspeaker arrays in terms of achieving a desired directivity behavior across the frequency domain used, the influence of the reproduction room as well as errors resulting from a limited robustness of the beamforming filters toward deviations of the loudspeakers, the signal amplitudes, etc. Thus, the possibilities of spatially selective reproduction via physical measures and measures related to signal processing are limited.
It would be desirable to have a concept for spatially selective audio reproduction that enables achieving a more clear-cut separation, at a specific region of a sonication area, of an audio signal provided for this region from one or more other audio signals that are reproduced in a superimposed manner.